Double-acting two-stroke internal combustion engine



Feb. 26, 1935.

DOUBLE-ACTING TWO-STROKE INTERNAL COMBUSTION ENGINE Filed Sept. 21, 1931 2 Sheets-Sheet 1- c. SCHAER 1,992,328

Feb. 26, 1935. c. SCHAER STROKE INTERNAL comsusnou ENGIN DOUBLE-ACTING TWO- 2 Sheets-Sheet 2 Filed Sept. 21, 4931 INVENTUF I with the respective working Patented I F 26,1935

Donate-Acme Charles Schaer, signor to the Application Sep stroke internal combustion its object the modification of the ports associated with the two engines and has for of the characteristics combustion chambers of a cylinder to compensate more fully abscissae against instantaneous areas of than hitherto for the diil'e tics betweensuch working In the following description and claims,'reierrence in characterischambers.

ence will be made to the area-time integral 0! a porter ports. If, for a port, intervals of time (or crank angles in the case 01' an engine running at constant revolutions) are plotted as port opening as ordinates, a curve is obtained beginning and ending on the enclosed between such abscissaaxis. The area curves and the abscissa axis is a measure of the charge admitted or released by such port, and will be hereinafter re:

ferred to as the area-time integral.

To show the area-time interval or ports per .unit of volgime of the working chamber, the same -intervals of time as above are plotted as abscissae against ordinates being a measure oi thesame instantaneous areas of port opening uncovered by the piston or other control member divided by the total volume cerned'. This volume and on the other side of the working chamber conon one side of the piston is ,the product oi cross-section and piston stroke,

of the piston is the same value reduced by the product of the cross-section of the piston rod and volume of the piston rod.

It has previously been pr the type under discussion, t difference mvolumes betw the piston-stroke, i. e., the

oposed, in engines of o compensate for the een the two working chambers of a cylinder, occasioned by the passage of the piston rod through one of th'em,.by reducing the area-time integral of ports associated with this chamber to a value such that ing chambereare ports associated chambers.

unit volume of work- It has now been found that such reduction is insufllcient in that, whilst compensating for the volumetric diflerence referred to no account is taken of the diiference in combustion conditions in the two working chambers. In particular the travel the combustion chamber runs appreciably cooler sed by the piston rod n the other since the piston rod oiiers extraconduction surface and the stufiing boxes must be kept well cooled to avoid damage thereto. Thus the work done per unit volume of this working that obtainable in the 0th chamber is less than erv working chamber.

rso STATES... Mrs Ni oFFica Two-smoke COMBUSTION ENGINE Switzerland, asflrm oi Stiller Anonymc, Winterthhr, Switzerland tember 21, .1931, Serial No. In Switzerland september 25, .1930

6 Claims. ion. its-s1) g with .the ports functioning as previousmanor Frres' socit Further, 1y proposed, additional losses occur since the expansion in the cooler working chamber is stopped too early and the scavenging air consumption is excessive in comparison able In addition this excess of scavenging air causes an excessive consumption of fuel and results in uneconomical running of the engin The present invention has for its principal object to compensate for these additional dinerences in characteristics between the two working chambers of the cylinder, and in contrast with previous proposals consists in a double-acting two-stroke internal combustion engine in which ports of that working chamber of the cylinder which is traversed by the piston rod have area-time integrals-per unit volume of working chamber which are smaller than the similar integrals of corresponding ports in the other working chamber by an amount such that, in addition to the compensation made in the known manner for the decrease in volume 01' the combustion chamber owing to the presence of the piston rod, compensation is made for the unfavourable thermal conditions and the conditions governing dim with the work obtainthe gas flow imposed by the presence of the piston rod.

The specified difierence between ports as to their area-time integrals per unit volume oi. combustion chamber can obviously be established as regards the inlet ports associated with the two working chambers, or the outlet ports or both inlet and outlet ports.

Further, the means whereby this difference can be established may be various, as indicated hereinafter, but by way of example a convenient embodiment of the invention is hereinafter described and shown in the accompanying drawings, in which,

Figures 1 and 2 are graphs showing the port opening per unit volume of combustion chamber plotted against time or crank angle.

If F is used to represent-the admission or outlet member, referred to the unit chamber concerned Accordingly the diagram the piston combustion gases will be able to escape from the greater to suit the engine through opening area uncovered by the piston or other control member at each movement or at each value of crank angle, and V the real volume of working chamber as previously referred to for one side or for the other side of the piston, the ordinates V A will represent the admission or outlet opening area at each moment or value of crank angle and uncovered by the piston or. other control.

volume of the workareas enclosed by the curves, represent the area-time integral per unit volume,-which is represented by V A V The curves in Figures 1 and 2 are those for a double-acting two-stroke internal combustion engine with the usual admission and outlet ports which are controlled by-the piston alone. The height of the exhaust ports is made as usual, pressure conditions, than the height of the admissionvports. .The combustion air is admitted into the working the admission ports. The piston on rising, will close the admission ports and begin to compress the combustion air contained in the working chamber. At or about the dead centre at which the ports are closed by the piston, there is injected into the highly compressed combustion air any desired fuel, which can be ignited by the compression heat alone or by means of separate auxiliary devices.

During the expansion or working stroke following the compression stroke, the combustion gases generated will expand and transmit to the piston the work contained in them. As soon as begins to uncover the outlet ports, the

working chamber and afterwards when the admission ports have also been uncovered by the piston they will be completely swept out from the working chamber by the scavenging air entering through the said ports. The scavenging or com- I begin again:

The curves 1 bustionair which is now contained in the working chamber,- will be again compressed after first the admission ports and then the outlet ports are closed by the piston, whereupon the cycle will is not traversed by the piston rod, whilst the curves 2 and 4 shown in chain-dotted lines, belong tothe other working chamber traversed by the piston rod. The dead centres corresponding to these processes in the two cylinder ends Ire,

during the working of the engine, displaced by section of opening of the outlet ports, which is obtained at the'point O, referred to the unit volume of the chamber, is calculated in such a manner that during the time from A or A to O,

and 3 shown in full lines in 'l ig- .ures 1 and 2, refer to the working chamber which chambers of the at the point Z or Z V the admission the pressure of the combustion gases in the working chambers has fallen at least to the pressure of the scavenging air, in order to prevent any flowing back of the combustion gases into the scavenging air conduits. After the point 0, the cross-section of the outlet ports can of course increase still further until after the ports have been completely uncovered by the. piston, it

reaches the value 0 or 0 Y The opening of the admission ports, which begins at the points A or A starts the scavenging of the working chamber in order completely to expel from the working chamber any combustion the areas enclosed in Figure 1 between .dmission ports, and at the f. outlet ports are closed whereof the combustion air inthe curves 1 or 2 and the axis of abscissa, represent the'share of the area-time integrals (for of the air) per unit volume of working chamber, and the areas enclosed in Figure 2 between the curves 3 or 4 and the axis of the abscissae, represent the area-timeinte'gral (for release of combustion gases) per unit volume of working: chamber. I

According to the invention, the value of such integral for the outlet ports (curve 4) associated with the working chamber traversed by the piston rod, is made smaller than the value of such integral-for the outlet ports (curve 3) associated with that working chamber not traversed by the piston rod. Owing to this difference, the advan: tage is obtained that in traversed by the piston rod, the outlet openings are not opened too early, thereby avoiding a premature escape of the high can still transmit fore avoiding an by such escape, and this extra work is now transmitted to thecrank shaft of the engine.

The most favourable conditions for ing chamber will be obtained additional loss of work caused the working chamber pressure gases, which work to the piston and there-' the work- I when the excess of formed per chambers. ber traversed by unit volume of the said working As this work in the working chamthe piston rod is smaller than in the other working chamber not traversed by the piston rod, hilst the admission openings per unit volume are made the same for both working chambers (curves .1 and 2, Figure 1) the reduction in the excess of scavenging air is obtained by a smaller scavenging pressure in front of the corresponding admission portsfor the working chamber traversed by the piston rod.

Instead of making the scavenging pressure for one working chamber lower than for the other, the samescavenging pressure may be of course used simultaneously for both w'orkingchambers, and an increase in the excess of scavenging air in the working chamber not traversed by the pis ton rod, can be obtained, according to the invention, by an additional charging with scavenging air or by 'super'charging with air of higher pressure. For this purpose, separate scavengthe closing of the outlet ports of the chamber not traversed by the piston rod, ,by liiting. air admission openings are opened at the point B (Figure 1) at the moment of, or after, working ing a control member such as for instance a valve, which admits additional or supercharging air into the cylinder until such ports are closed by the piston at C.

chamber not traversed by the piston rod, and the diagram areas enclosed by the curves 2 and 4 represent the area-time integrals per unit volworking chamber traversed by the According to the invention, the areas enclosed by the chain-dotted curves 2 or 4, are smaller than the areas enclosed by the curves 1 and 5 or 3 shown in full lines.

The cylinder 20 of the internal combustion engine shown in Figure 3 and taken as the basis for the curves of Figures 4 and 5, is supplied with the scavenging air through a pipe 21 connected to'the working cylinder 20, whilst the combustion gases generated in the cylinder, are discharged through the exhaust conduit 22. piston 23 which is shownin dead centre position,

The

uncovers in this position for the upper working chamber 24 the noncontrolled admission port series 25, the controlled admission port series 26 and the outlet port series 27. The residue of the waste gases still contained in the upper combustion chamber 24 is expelled through the outlet ports 27 into the waste gas conduit 22 by the scavenging air entering directly through the ports 25 and the non return valve 28.

In the upper dead centre position of the piston 23, shown inchaih-dotted lines, the piston controlled admission ports 25, the admission ports 30 controlled by a valve 29 and the outlet ports 31, are uncovered in the same way for the lower working chamber traversed by'the piston rod 32.

The admission ports 25, 26 and 30, as well as the outlet ports 27 and 31, are arranged symmetrically to the plane I-I at right angles to the cylinder axis. The bottom dead centre po- SltlOIl shown in full lines, and the upper dead centre position shown in'chain-dotted lines, are

however arranged symmetrically to another plane IIII which is also at right angles to the cylinder axis, the two planes of symmetry I--I and II-II being parallel to each other at. a distance apart it. This ensures that according to the invention the area-time integrals per unit volume of working chamber are smaller for the lower working chamber than for the upper combustion chamber 24.

For the upper end, the controlled air admission ports 26 are uncovered already at the moment A Figure 4, but as the excess of pressure of the combustion gases in the cylinder prevents the opening of the scavenging valves 28 arranged in front of the ports 26, no air will yet enter the cylinder. The corresponding outlet ports 27 are opened at the moment A Figure 5. At the moment when the pressure in the cylinder has fallen to. a sufficient extent, the scavenging valves 28 for the ports 26, as well as the ports 25, will be opened. At the moment 2, the ports 25 will be closed, whilst scavenging through the air admission ports 26 will still continue during closing of the outlet ports at Z". Until the moment Z these air admission ports 26 will remain open, so that during the -interval from Z -Z dotted curves 7, 9-and 11.

full lines in the lower bustion engine as recited there will take place additional charging of the working chamber 24.

The corresponding scavenging, charging and I exhaust processes for the lower cylinder end, governed by the sponding manner in Figures 4 and by the chain Their shape is the same as that of the curves 6, 8 and shown in full lines. According to the invention-however, the areas enclosed between the axis of the abscissae and the chain-dotted vcurves 7, 9, 11

ing chamber in the upper cylinder end.

If desired, the planes of symmetry 1, of the ports and that H of the of the piston could be unit volume of working chamber may be produced by the diflerence in the nature of the piston movements at or about the two dead centre positions caused by the finite length of the connecting rod. Of course the admission ports could also be given any desired shape and arrangement and if desired, the ports could be posiand closed in by suitably controlled members in order to ensure additional charging or to prevent exhaust gases from entering the scavenging air conduits, or in order to'ensure other special conditions of opening. If desired certain ports could be made operative both for the upper and for the lower cylinder ends.

I claim:

1. A double-acting, two-stroke, internal comworking chamber traversed by the piston rod, said chamber having ports, another working chamber having ports, said first ports having area-time integrals per unit-volume of the, first chamber which are smaller corresponding ports in such an amount as to compensate for the decrease in volume of the working chamber due to the piston rod therein, and for piston-rod produced unfavorable thermal conditions and unfavorable conditions governing the gas flow.

2. A double-acting, two-stroke, internal' combustion engine as in claim 1,'in which the respective ports for the respective working chambers are located at or about the two dead-center positions respectively.

3. Adouble-acting, two-stroke, internal comin claim l, in which means are provided for establishing said difierence in area-time integrals per. unit-volume of combustion chamber both for the inlet ports and for theoutlet ports in the respective working chambers.

4. A double-acting, two stroke, internal combustion engine as recited in claim 1, in which said any desired manner the upper piston edge when in the lower dead center position, such displacement being to the extent necessary to establish the specified difference in area-time integrals per unit'volume o! combustion chamber.

5. A double-acting, two-stroke, internal combustion engine as recited in claim 1, in which. means are provided for supplying auxiliary air to that one of the working chambers which isnot traversed by the piston-rod, supplying it only after chamber.

6. A double-acting, two-stroke,'internal com-' bustion engine as recited in claim 1, in which means are provided for rendering the pressure of the scavenging air for the working chamber traversed by the piston-rod, lower than that at which scavenging air is supplied to the other combustion chamber.

closure 01 the outlet ports ior this said:

CHARLES SCH'AER. 10 

